Nullable enum in html helper

Question

I have a view model that contains enum with nullable type like this one :

public StudyLevel? studyLevel { get; set; }

I have made custom html helper to display a dropdownlist for rendering the enum into the view, the nullable case is displayed using

<option value="null">No value</option>

the problem is that when i submit the form modelstate give me the error :

studylevel cannot be "null" .

Could you suggest me any way to help me handle the nullable type in the view ?

Answer 1

I might be wrong but I am pretty sure there are some limitations around nullable enums and the MVC default model binder. I would recommend having a state which represents " no value " instead eg

StudyLevel.None

That way you don't need to deal with checking for null etc.

Answer 2

What if you change your html helper to display the null value like this?

<option>No value</option>

Or like this?

<option value="">No value</option>

Edit: A better option (IMO) is to create a collection of SelectListItem and then use a built-in HTML helper. Please take a look into this article I created some months ago, it may help you. You can use it like this:

@Html.EnumDropDownList<StudyLevel?>("studyLevel", "No value")

More info here:

ASP.NET MVC: Creating localized DropDownLists for enums